1. Field of the Invention
This invention relates generally to an automatic servo gain control system for an optical disk player apparatus and, more specifically, to an automatic servo gain control system to be used in servo loop that performs positional adjustments of an optical head relative to a optical disk for maintaining the open loop servo gain constant.
2. Description of the Background Art
In an optical disk player apparatus there is known a focus servo system and a tracking servo system for making positional adjustments of the optical head relative to the optical disk. In such servo systems there has been proposed an automatic servo gain control system that automatically controls the gain for a positional error signal, such as a focus error signal or a tracking error signal, in response to a parameter variation, such as variations in the intensity of a light beam reflected from the optical disk due to different operational modes, such as recording, reproduction, and erasing. More specifically because the intensity of the light beam irradiated onto the optical disk is controlled to be at different levels according to the particular operational mode, variations in reflectance of the optical disks can be used in the servo system.
One conventional automatic servo gain control system detects the peak-to-peak value of an S-shaped focus error signal and the peak-to-peak value of a tracking error signal produced as the head traverses the tracks. The system controls the respective peak-to-peak values to be constant so as to perform automatic gain control of the positional error signals.
Although such conventional automatic servo gain control system is capable of dealing with the above-mentioned parameter variations relative to different operational modes, it is unable to deal with variations in the gain or other characteristics of the optical head actuator. Of course, because the optical head actuator gain affects the open-loop gain of the servo loop, the conventional system is unable to provide a constant open-loop gain when the optical head actuator gain varies. Accordingly, the conventional servo gain control system can not provide a stable and reliable optical head servo system that can take into account all possible parameter variations, including variations in the optical head actuator gain.